Method of controlling a polymerization reactor

ABSTRACT

The present invention provides methods of controlling a gas-phase polymerization process. The method includes determining a difference between a control variable of the polymerization process, such as the production rate, and the desired value of the control variable; adjusting or maintaining a first manipulated variable to at least partially compensate for the difference between the control variable and the desired value; and adjusting or maintaining a second manipulated variable to at least partially compensate for the effect of adjusting or maintaining the first manipulated variable. The first and second manipulated variables can include process variables such as the fluidized bed weight, the catalyst concentration, the concentration of one or more monomers, the flow of one or more comonomers, the ratio of one comonomer to another comonomer, the activator concentration, the ratio of an activator to selectivity control agent, the concentration of a chain transfer agent, and the retardant concentration.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of the U.S.application Ser. No. 11/666,723, filed on Apr. 30, 2007, now U.S. Pat.No. 8,093,341, issued on Jan. 10, 2012, entitled “METHOD OF CONTROLLINGA POLYMERIZATION REACTOR,” the teachings of which are incorporated byreference herein, as if reproduced in full hereinbelow, which is a 371national phase application of International Patent Application No.PCT/US05/37338, filed on Oct. 18, 2005, which claims priority from theU.S. Provisional Application No. 60/622,755, filed on Oct. 28, 2004, theteachings of which are incorporated by reference herein, as ifreproduced in full hereinbelow.

TECHNICAL FIELD

The invention relates to the control of gas-phase polymerizationprocesses in the presence of a catalyst through the coordinatedmanipulation of selected process variables.

BACKGROUND ART

In a highly competitive market, olefin polymerization reaction systemsare pushed ever closer to their operating constraints in order toincrease production in existing equipment. Operating close to theconstraints, the possibility of a reactor upset becomes greater. Anupset is a reaction which deviates from normal operating constraints toa degree which requires a correction in production rate to prevent asignificant economic loss by way of a shutdown, production of unusableproduct, loss of raw material, or the like. Thus, it is important tocontrol upsets which would otherwise require a shutdown or other drasticor unusual operating action unless an effective amount of polymerizationretarding agent is introduced imminently. Typically an upset couldinvolve a significant increase in temperature in the reacting system,which may escalate the reaction further out of control and/ordangerously soften the product particles, causing them to stick togetherand form large unmanageable agglomerates. Unusual pressure values,superficial gas velocities, or static effects can also be harbingers ofupsets, although not as common or always as dependable as temperatures.Upsets can also be the result of influences that are not measured orpredicted, such as variations in reactant feed quality, irregularcatalyst flow(s), and equipment malfunction. To maintain reactoroperation and avoid expensive shutdowns, polymerization retarders can befed into the reactor during or following an upset once it is detected,but manual intervention to introduce fast acting polymerizationretardants may often not be timely enough or accurate enough to avoidthe adverse consequences of major process upsets. Human monitoringcannot be expected to suffice where combinations of rapidly changingvariables must be interpreted to anticipate runaway conditions.

One method for controlling reactors uses neural net based controllers. Aneural network is an interconnected assembly of simple processingelements, units or nodes, whose functionality is loosely based on theanimal neuron. The processing ability of the network is stored in theinter-unit connection strengths, or weights, obtained by a process ofadaptation to, or learning from, a set of training patterns. In neutralnet systems, a collection of process inputs and controllers aresimultaneously used and controlled because of the nature of neural netsto achieve the improvement. Thus, when the controller is turned off,there is no effective control of resin properties, control of pressure,control of production rate, optimization of production rate. When thecontroller is activated, the multiple inputs and process variables areevaluated and the collective nature of these values results in a controleffort. It would be desirable to provide a method that can controlprocess variables without using a neural net approach.

DISCLOSURE OF INVENTION

Embodiments of the invention provide a method of controlling a gas-phasepolymerization process that includes (a) continuously, periodically orintermittently determining a difference between an actual or estimatedvalue of a control variable of the polymerization process and a desiredvalue of the control variable of the polymerization process; (b)adjusting or maintaining at least a first manipulated variable to atleast partially compensate for the difference between the actual orestimated value of control variable and the desired value; and (c)adjusting or maintaining a second manipulated variable to at leastpartially compensate for the effect of adjusting or maintaining thefirst manipulated variable. The first and second manipulated variablesare selected from the group of process conditions consisting of a weightof fluidized bed, a catalyst concentration, a concentration of one ormore monomers, a flow of one or more comonomers, a ratio of a firstcomonomer to a second comonomer, a first activator concentration, aratio of a second activator to selectivity control agent, aconcentration of a chain transfer agent, and a retardant concentration.

In particular embodiments, the control variable is the production rate.Some embodiments, where the production rate is the control variable, cancontrol the production rate within an average of 10% of the desiredproduction rate when measured over an 8 hour period. In someembodiments, the average production rate deviates from the desiredproduction rate by less than 8%, preferably less than 5% of the desiredproduction rate when the average is measured over an 8 hour period. Inother embodiments, the control variable can be a resin property such asthe molecular weight, the melt index, or molecular weight distributionof the resin.

In particular embodiments, the invention is a method of controlling theproduction rate of a polymerization process that includes (a)determining a desired value of the production rate; (b) continuously,periodically or intermittently monitoring the actual or estimated valueof the production rate of the process; (c) continuously, periodically orintermittently comparing the actual or estimated value of the productionrate to the desired value of the production rate; (d) adjusting ormaintaining at least a first manipulated variable to at least partiallycompensate for the difference between the actual or estimated value ofthe production rate and the desired value; and (e) adjusting ormaintaining a second manipulated variable to at least partiallycompensate for the effect of adjusting or maintaining the firstmanipulated variable, wherein the first and second manipulated variablesare selected from the group of process conditions consisting of a weightof fluidized bed, a catalyst concentration, a concentration of one ormore monomers, a flow of one or more comonomers, a ratio of a firstmonomer to a second monomer, an activator concentration, and a retardantconcentration; and wherein an average production rate determined over atleast about 8 hours is within about 10%, preferably within 8%, morepreferably within 5% of the desired value of the production rate.

In other embodiments, the invention provides a method of controlling theproduction rate in a gas-phase polymerization process, wherein themethod comprises (a) determining a desired value of the production rate;(b) continuously, periodically or intermittently monitoring the actualor estimated production rate; (c) continuously, periodically orintermittently determining a difference between the actual or estimatedproduction rate and the desired value; (d) adjusting or maintaining atleast a first manipulated variable within a range having an upper and alower limit to at least partially compensate for the difference betweenthe actual or estimated production rate and the desired value; and (e)continuously, periodically, or intermittently adjusting or maintainingthe second manipulated variable within a range having an upper and alower limit around a target value for the second manipulated variable toat least partially compensate for the effect of adjusting or maintainingthe first manipulated variable and to at least partially compensate fora remaining difference between the actual or estimated production rateand the desired value; wherein the first and second manipulatedvariables are selected from the group of process conditions consistingof a weight of fluidized bed, a catalyst concentration, a concentrationof one or more monomers, an activator concentration, and a retardantconcentration with the proviso that when the first manipulated variableis the catalyst concentration, the second manipulated variable isselected from the group consisting of the weight of fluidized bed, theactivator concentration, and the retardant concentration.

In some embodiments, the process provides for controlling one controlvariable of a polymerization reactor independently of controlling otherpolymerization conditions.

In some embodiments compensating for the effect of adjusting the firstmanipulated variable further includes compensating for at least aportion of a remaining difference between the actual or estimated valueof the control variable and the desired value.

Some of the methods can also include establishing limits on the value ofthe first manipulated variable.

Some of the methods described of above include adjusting the secondmanipulated variable continuously, periodically, or intermittently ormaintaining the second manipulated variable within a range having anupper and a lower limit bounding a target value for second manipulatedvariable. When such a range is employed, the upper and lower limits maydiffer in their relative distance from the target value. In other words,the absolute value of the difference between the upper limit and thetarget value is different than the absolute value between the lowerlimit and the target value. Thus, in some embodiments, one limit may beset to allow a relatively smaller deviation from the target value whilethe other limit allows a relatively larger deviation. Regardless of thevarious limits that may be chosen, the target value of the secondmanipulated variable can be adjusted at various times during theprocess. In some embodiments, the target value of the second manipulatedvariable is continuously updated or adjusted. In others it may beintermittently or periodically updated or adjusted.

Some embodiments of the process are not limited by the type of catalystthat may be used, but some processes of the invention are particularlywell-suited to single site catalysts. In particular embodiments, thesingle site catalyst is metallocene catalyst. In other embodiments, aZiegler-Natta catalyst may be used. Some embodiments can also be appliedto processes using a chrome catalyst.

Particular combinations of first and second variables are also preferredin some embodiments. For example, in some preferred embodiments, thefirst or second manipulated variable is the fluidized bed weight. Insome methods described herein, the first and second manipulatedvariables are the catalyst concentration and the fluidized bed weight.In other embodiments, the first and second manipulated variables are theactivator concentration and the fluidized bed weight. In still otherembodiments, the first and second manipulated variables are theconcentration of one or more monomers and the fluidized bed weight. Yetother embodiments use the fluidized bed weight and the retardantconcentration as the first and second manipulated variables. In someembodiments where the bed weight is manipulated, the bed weight ismaintained within about 5% of a target bed weight. In other embodiments,the bed weight is maintained within 1%, 2%, 3%, or 4% of the target bedweight of the control process. The first and second manipulatedvariables may also be the catalyst concentration and the concentrationof one or more monomers. In some particularly useful embodiments of theinvention, the first and second manipulated variables are selected sothat when the first manipulated variable is the catalyst concentration,the second manipulated variable is selected from the group consisting ofthe weight of fluidized bed, the activator concentration, and theretardant concentration.

Embodiments of the invention described above may account for therelative speed with which a change in a manipulated variable produces aneffect on the first process condition. Typically, the variables areselected so that a change in the second manipulated variable affects thecontrol variable relatively faster than a change in the firstmanipulated variable. But in some embodiments, the first manipulatedvariable may be slower acting than the second manipulated variable, orthe manipulated variables can affect the first process condition inabout the same amount of time.

The methods described above can be used in polymerization processes toprepare a variety of products. Some preferred methods are used in theprocesses that make an alpha-olefin homopolymer or interpolymer. Somemethods are particularly suited to processes for preparing apolyethylene homopolymer or an interpolymer of ethylene with at leastone comonomer selected from the group consisting of a C₄-C₂₀ linear,branched or cyclic diene, vinyl acetate, and a compound represented bythe formula H₂C═CHR wherein R is a C₁-C₂₀ linear, branched or cyclicalkyl group or a C₆-C₂₀ aryl group.

Other methods are particularly useful for processes for preparing apolypropylene homopolymer or an interpolymer of propylene with at leastone comonomer selected from the group consisting of ethylene, a C₄-C₂₀linear, branched or cyclic diene, and a compound represented by theformula H₂C═CHR wherein R is a C₁-C₂₀ linear, branched or cyclic alkylgroup or a C₆-C₂₀ aryl group. In one such method the second manipulatedvariable is the ratio of activator to selectivity control agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a fluidized bed reaction system useful withembodiments of the inventive catalysts.

FIG. 2 illustrates the effect of the bed weight in an embodiment of theinvention where the bed weight and a comonomer partial pressuremanipulated to control the polymerization process.

FIG. 3 illustrates the effect of the comonomer partial pressure in anembodiment of the invention where the bed weight and a comonomer partialpressure manipulated to control the polymerization process.

FIG. 4 illustrates the effect of the catalyst flow in an embodiment ofthe invention where the catalyst flow and a comonomer partial pressuremanipulated to control a metallocene-based polymerization process.

FIG. 5 illustrates the effect of the comonomer partial pressure in anembodiment of the invention where the catalyst flow and the comonomerpartial pressure manipulated to control a metallocene-basedpolymerization process.

MODES FOR CARRYING OUT THE INVENTION

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or“approximately” is used in connection therewith. They may vary by up to1%, 2%, 5%, or sometimes 10 to 20%. Whenever a numerical range with alower limit, RL, and an upper limit RU, is disclosed, any number Rfalling within the range is specifically disclosed. In particular, thefollowing numbers R within the range are specifically disclosed:R=RL+k*(RU−RL), where k is a variable ranging from 1% to 100% with a 1%increment, i.e. k is 1%, 2%, 3%, 4%, 5%, . . . , 50%, 51%, 52%, . . . ,95%, 96%, 97%, 98%, 99%, or 100%. Moreover, any numerical range definedby two numbers, R, as defined above is also specifically disclosed.

Described herein is a process for controlling the polymerization of oneor more alpha-olefins in the gas phase in the presence of a catalyst. Ina broad sense, embodiments of the invention provide a method thatincludes (a) continuously, periodically or intermittently determining adifference between an actual or estimated value of a control variable ofthe polymerization process and a desired value of the control variableof the polymerization process; (b) adjusting or maintaining at least afirst manipulated variable to at least partially compensate for thedifference between the actual or estimated value of control variable andthe desired value; and (c) adjusting or maintaining a second manipulatedvariable to at least partially compensate for the effect of adjusting ormaintaining the first manipulated variable. The first and secondmanipulated variables are selected from the group of process conditionsconsisting of a weight of fluidized bed, a catalyst concentration, aconcentration of one or more monomers, a flow of one or more comonomers,a ratio of a first comonomer to a second comonomer, an activatorconcentration, a ratio of an activator to selectivity control agent, aconcentration of a chain transfer agent, and a retardant concentration.

One method of controlling processes is a modular multivariable controlsystem (“MMC”). A modular multivariable control system is aninterconnection of one or more individual controllers, calledcoordinated controllers. One such system is described in U.S. Pat. No.5,191,521, incorporated herein by reference in its entirety. Typically,each coordinated controller effects the control of one process variablein a process through any number of control efforts. Consequently, ifthere are, say, three process variables to be monitored and controlledin a process, there will be three interconnected coordinated controllersmaking up the MMC system which controls that process.

A process model is constructed for the coordinated control structure.The process model describes the influence that each adjustment ormaintenance of a manipulated variable has upon the process (first)condition, and the time period elapsed before that influence isreflected in the process condition. This time period from when anadjustment or maintenance of a manipulated variable is changed until aresultant effect is exhibited in the control process condition is calledthe “dead time” for that adjustment or maintenance of a manipulatedvariable. Therefore the adjustment or maintenance of the secondmanipulated variable is effectively performed on the remainingdifference between the actual or estimated value of the processcondition and its desired value or condition, called its set point. Eachadjustment or maintenance of a manipulated variable associated with aparticular coordinated controller may, and ordinarily does, have adifferent respective dead time.

Filters are configured for each manipulated variable and are used totune the controller response to process condition changes. Filtersdescribe how or along what trajectory the process condition willprogress toward its set point given a change in the process, such asthat due to a disturbance or a change in the set point. Each filter hasa tuning parameter corresponding to its respective adjustment ormaintenance of a manipulated variable which determines the rate at whichthe process condition will progress toward this set point. These tuningparameters accommodate modeling errors by matching the speed of responseof the process condition to the expected modeling error. Large modelingerrors require the associated response to be tuned to be relatively slowto prevent unstable or oscillatory responses to a disturbance or setpoint change. Conversely, small modeling errors permit tuning theresponse to be relatively fast, thus allowing a quick response to systemchanges.

Each adjustment or maintenance of a manipulated variable whichinfluences the process condition is given a ranking which indicates itslong term ordering relative to the other adjustment or maintenance ofmanipulated variables. The lowest order long term, or primary,adjustment or maintenance of a manipulated variable is that adjustmentor maintenance of a manipulated variable which assumes the long termload necessary to maintain the process condition at its set point.Contributions to the long term load are made by the higher order,secondary, long term adjustment or maintenance of manipulated variablesonly if the primary has saturated, i.e., reached its limit. The primaryadjustment or maintenance of a manipulated variable is preferably onethat is easily and inexpensively supplied relative to the otheradjustment or maintenance of other manipulated variables.

Each adjustment or maintenance of a manipulated variable is also given aranking which indicates its short term ordering relative to the otheradjustment or maintenance of manipulated variables. The lowest orderactive adjustment or maintenance of a manipulated variable, or the firstactive adjustment or maintenance of a manipulated variable, is thatwhich will respond towards the short term change, such as a change ofset point or the entering of a disturbance, to drive the processcondition to its set point. The higher order active adjustment ormaintenance of manipulated variables, i.e., secondary active control,will be used to compensate for short term change only if the lower orderactive control (first active control) has saturated. In general, it ispreferable to choose the first active control as the one that can forcethe process condition to respond most rapidly to set point changes anddisturbances. Note, in some cases, it may be desirable to have two ormore adjustment or maintenance of manipulated variables actsimultaneously. In such a case these adjustment or maintenance of amanipulated variables would be given the same active order number.

In the case where no adjustment or maintenance of manipulated variableshave saturated, a coordinated controller having “n” associatedadjustment or maintenance of manipulated variables is capable ofmaintaining the process condition at its respective set point whilekeeping n−1 adjustment or maintenance of manipulated variables at theirdesired values (in accordance with mathematical convention, the letter“n” represents any whole number). In general, secondary and higher orderlong term adjustment or maintenance of manipulated variables areassigned desired nominal values at which they are maintained unless theyare needed to suppress long term load disturbances or to achieve thedesired set point. Each adjustment or maintenance of a manipulatedvariable further has a prescribed limit to which it can be adjusted fromits nominal value. For example, if the adjustment or maintenance of amanipulated variable is a valve, the nominal value may correspond to aposition where the valve is half open, and the limit would thencorrespond to that adjustment which would fully open or fully close thevalve. Consequently, unless the primary adjustment or maintenance of amanipulated variable has been saturated, the secondary and higher orderlong term adjustment or maintenance of manipulated variables will beadjusted so as to reach their nominal values in the long term.

The first active control can be either the primary, secondary or higherorder long term adjustment or maintenance of a manipulated variable. Ifit is the primary, then all other adjustment or maintenance ofmanipulated variables will be maintained at their nominal values. If thefirst active control is a secondary or higher order longer term control,when the first active control is adjusted to obtain the desired responsefor the process condition, the primary control will also be adjusted sothat the first active adjustment or maintenance of a manipulatedvariable will eventually return to its desired nominal value.

By combining the respective influences of the individual adjustment ormaintenance of manipulated variables, the process condition may bemaintained at the chosen set point over both the short and long termirrespective of process disturbances. When a disturbance is detected inthe process, such as through a decrease in the process condition, thefirst active adjustment or maintenance of a manipulated variable isadjusted to compensate for that decrease. The progressively higherpriority active adjustment or maintenance of manipulated variables arealso adjusted to compensate for the decrease only as lower order activeadjustment or maintenance of manipulated variables become saturated.Concurrent with the adjustment of any lower order active adjustment ormaintenance of a manipulated variable, the primary adjustment ormaintenance of a manipulated variable is adjusted to compensate for thedisturbance in the long term regardless of the short term adjustmentsmade to the other adjustment or maintenance of manipulated variables. Astime progresses and the primary adjustment or maintenance of amanipulated variable begins to exhibit its influence on the processcondition, the lower order active adjustment or maintenance ofmanipulated variables initially used to compensate for the disturbanceare returned to their nominal values.

The production rate, or other variable can be continuously, periodicallyor intermittently monitored. Typically, the monitoring is accomplishedby a numerical model to give a cumulative or instantaneous approximationof the value of the control variable in the process. In otherembodiments, the value of the control variable can be measured directly.But in some embodiments, it is preferable to monitor the controlvariable based on an instantaneous measure of its value. Methods fordetermining instantaneous values of process variables such as productionrate are known in the art. Regardless, of how it is determined, thevalue of the control variable is compared to the desired value of thecontrol variable. The value of the control variable can be essentiallycontinuously compared to the desired value. But typically, thecomparison is made at regular intervals at a predetermined periodicity.In other embodiments, the value is compared to the target rangeintermittently based typically on other process condition indicatorsthat may signal the possibility of a deviation of the control variablefrom its desired value. The desired production rate in pounds per hourtypically ranges from about 3,000 to about 250,000 pounds per hour, andis preferably in the range of about 8,000 to about 140,000 pounds perhour. This range is proportional to the size of reactors thus, largerreactor are capable of higher productions rates.

Once the desired resin production rate is determined, the actualproduction rate is observed as the polymerization progresses. One way ofdetecting the actual production rate is accomplished by detectingchanges in the exotherm of the reaction and calculating a productionrate based on these changes. When the value of the control variable isnot at the desired value, a process variable is adjusted or maintained.A first process variable is adjusted or maintained to at least partiallycompensate for the difference between the value of the control variableand its desired value. In addition, a second process variable isadjusted or maintained. The second variable is adjusted or maintained toaccount for the effect that a change to the first variable has on thereaction system and in some embodiments to compensate for at least apart of the remaining difference between the value of the controlvariable and the desired value of the control variable. Processvariables that are adjusted in an effort to move the control variabletoward its desired value are referred to as manipulated variables.

Selection of pairs of first and second manipulated variables is made bymodels that predict the effects of such changes in process variables,disturbances, or set point changes will have on the control variable.The models have a tuning parameter corresponding to its respectivecontrol effort for each of the manipulated variables which determinesthe rate at which the process variable will progress toward this setpoint. These tuning parameters accommodate modeling errors by matchingthe speed of response of the process variable to the expected modelingerror. Large modeling errors require the associated response to be tunedto be relatively slow to prevent unstable or oscillatory responses to adisturbance or set point change. Conversely, small modeling errorspermit tuning the response to be relatively fast, thus allowing a quickresponse to system changes. In some embodiments, the first manipulatedvariable is selected to have a relatively slower impact on the controlvariable. The second variable is typically selected to act over arelatively longer time scale. However, methods where the first variableis faster acting or acts on relatively the same time scale as the secondvariable are also possible.

The relative time-scale of a response due to a change in a manipulatedvariable depends on a number of factors. One factor is the so-called“dead time,” which is the time period from when a control action istaken until a resultant effect is exhibited in the value of the controlvariable. Each control action associated with a particular coordinatedcontroller may, and ordinarily does, have a different respective deadtime. For control actions influencing a multiplicity of processvariables, each will have a different model and a different dead timefor each process variable influenced. For example, an increase incatalyst concentration or flow will result in an increase in theproduction rate. However, the time it takes for the change inconcentration or flow is influenced by the time constant for thecatalyst. A typical time constant might be on the order of 100 minutesin addition to the time it takes to establish a meaningful concentrationchange. On the other hand an increase to the concentration, or flow, ofa monomer such as ethylene in an ethylene polymerization may produce anincrease in the production rate in about 10 to 15 minutes.

Typically, limits are set on the value the manipulated variable may takebefore corrective action is taken. Such limits around the desired valueof the manipulated variable can include distinct upper and lower limitsthat differ in their relative distance from the desired value. In otherwords, the absolute value of the difference between the upper limit andthe desired value of the manipulated variable is different than theabsolute value between the lower limit and the manipulated variable.Thus, in some embodiments, one limit may be set to allow a relativelysmaller deviation from the target value while the other limit allows arelatively larger deviation. Such limits are useful when a deviation inone direction from the desired value has a more critical effect on theprocess than a deviation in the other direction. Regardless, of thevarious limits that may be chosen, the desired value of the manipulatedvariable can be adjusted at various times during the process. In someembodiments, the desired value of the manipulated variable iscontinuously updated or adjusted. In others it may be intermittently orperiodically updated or adjusted.

Typical manipulated variables include process conditions such as theweight or level of the fluidized catalyst bed, the catalystconcentration, a concentration of one or more monomers, the flow of oneor more monomers, the ratio of one first monomer to a second monomer,the activator concentration, the ratio of the activator to selectivitycontrol agent, the concentration of a chain transfer agent, andretardant concentration. In one specific embodiment, the manipulatedvariables are any combination of these process conditions with theproviso that in a Ziegler-Natta process, embodiments other than thoseemploying catalyst concentration as the first variable and theconcentration of one or monomers as the second monomer are preferred. Inone specific embodiment, the method of controlling a control variable ofa polymerization reactor is independent of controlling otherpolymerization conditions in a gas-phase polymerization process.

In some methods the first and second manipulated variables are thecatalyst concentration and the fluidized bed weight. In otherembodiments, the first and second manipulated variables are theactivator concentration and the fluidized bed weight. In still otherembodiments, the first and second manipulated variables are theconcentration of one or more monomers and the fluidized bed weight. Yetother embodiments, use the fluidized bed weight and the retardantconcentration as the first and second manipulated variables. The firstand second manipulated variables may also be the catalyst concentrationand the concentration of one or more monomers. In some particularlyuseful embodiments of the invention, the first and second manipulatedvariables are selected so that when the first manipulated variable isthe catalyst concentration, the second manipulated variable is selectedfrom the group consisting of the weight of fluidized bed, the activatorconcentration, and the retardant concentration. In one specificembodiment, the process is a metallocene-catalyzed polymerizationwherein the first and second manipulated variables are selected suchthat when the one variable is the catalyst concentration, the othermanipulated variable is selected from the group consisting of the weightof fluidized bed, the activator concentration, and the retardantconcentration.

In some processes, manipulating the bed weight of the catalyst bed isparticularly useful in directing the value of the control variable whencoordinately adjusted along with another process condition. In someembodiments, the reactor bed weight operating point is set and theweight of the bed is allowed to vary as the models dictate, but isconstrained to a value within 1%, 2%, 5%, 8%, or 10% weight percent ofthe operating point. In some embodiments where the bed weight iscontrolled, the concentration of ethylene or propylene is alsocontrolled. Typically ethylene concentration is measured as its partialpressure. When propylene is used, the effect of liquid monomer in thereactor should also be accounted for. In certain embodiments, theconcentration of a monomer, particularly ethylene is maintained withinabout 50%, 35%, 25%, 20%, 10%, or about 5% of a target value. In onepreferred embodiment, the bed weight is increased and the ethyleneconcentration is reduced when the production rate exceeds the upperlimit on the production rate target range.

As mentioned above, some embodiments use changes in the concentration oramount of catalyst fed to the reactor to influence a control value, suchas the production rate. An increase in catalyst feed will increaseproduction rate and conversely a decrease in catalyst feed will decreaseproduction rate. By quantifying the manner in which the catalyst affectsthe production rate, the amount of catalyst needed to bring the actualproduction rate into line with the desired production rate isdetermined. In commercial processes, the catalyst can be fed into thereactor in a range of about 0 to about 250 pounds per hour, and ispreferably fed in a range of about 0 to about 100 pounds per hour. Thisrange is adjusted to reflect the productivity of the catalyst andprevent the overfeeding of catalyst to the reactor. The catalyst fedinto the reactor can, for short periods of time, be zero to compensatefor a much higher than desired production rate.

In some embodiments, the manipulated variables are coordinativelyadjusted or maintained in a manner designed to move the value of thecontrol variable within 1%, 2%, 5%, 8%, or 10% of the desired value ofthe control variable. Some control schemes can control the productionrate to within 1% or less of the selected production rate value onaverage when measured over an entire production run, typically 8 hours.Other control schemes can control the production rate to within 2%, 5%,8% or 10% of the selected production rate. Such averages should bedetermined on typical reactor runs over at least about an 8 hour periodof operation. In particular methods where the first and second variablesare the bed weight and the monomer flow, the production rate at anygiven point in the process does not exceed the target production rate bymore than about 25%. Other embodiments, may be able to control theprocess to a greater or lesser extent.

Examples of polymers that can be produced using the processes describedherein include homopolymers and copolymers (including elastomers) of analpha-olefin such as ethylene, propylene, 1-butene, 3-methyl-1-butene,4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene,1-decene, and 1-dodecene as typically represented by polyethylene,polypropylene, poly-1-butene, poly-3-methyl-1-butene,poly-3-methyl-1-pentene, poly-4-methyl-1-pentene, ethylene-propylenecopolymer, ethylene-1-butene copolymer, and propylene-1-butenecopolymer; copolymers (including elastomers) of an alpha-olefin with aconjugated or non-conjugated diene as typically represented byethylene-butadiene copolymer and ethylene-ethylidene norbornenecopolymer; and polyolefins (including elastomers) such as copolymers oftwo or more alpha-olefins with a conjugated or non-conjugated diene astypically represented by ethylene-propylene-butadiene copolymer,ethylene-propylene-dicyclopentadiene copolymer,ethylene-propylene-1,5-hexadiene copolymer, andethylene-propylene-ethylidene norbonene copolymer; ethylene-vinylcompound copolymers such as ethylene-vinyl acetate copolymer,ethylene-vinyl alcohol copolymer, ethylene-vinyl chloride copolymer,ethylene acrylic acid or ethylene-(meth)acrylic acid copolymers, andethylene-(meth)acrylate copolymer; styrenic copolymers (includingelastomers) such as polystyrene, ABS, acrylonitrile-styrene copolymer,α-methylstyrene-styrene copolymer; and styrene block copolymers(including elastomers) such as styrene-butadiene copolymer and hydratethereof, and styrene-isoprene-styrene triblock copolymer; polyvinylcompounds such as polyvinyl chloride, polyvinylidene chloride, vinylchloride-vinylidene chloride copolymer, polymethyl acrylate, andpolymethyl methacrylate; polyamides such as nylon 6, nylon 6, 6, andnylon 12; thermoplastic polyesters such as polyethylene terephthalateand polybutylene terephthalate; polycarbonate, polyphenylene oxide, andthe like. These resins may be used either alone or in combinations oftwo or more.

In particular embodiments, preferred polyolefins include polypropylene,polyethylene, and copolymers thereof and blends thereof, as well asethylene-propylene-diene terpolymers. In some embodiments, preferredolefinic polymers include homogeneous polymers described in U.S. Pat.No. 3,645,992 by Elston; high density polyethylene (HDPE) as describedin U.S. Pat. No. 4,076,698 to Anderson; heterogeneously branched linearlow density polyethylene (LLDPE); heterogeneously branched ultra lowlinear density (ULDPE); homogeneously branched, linearethylene/alpha-olefin copolymers; homogeneously branched, substantiallylinear ethylene/alpha-olefin polymers which can be prepared, forexample, by a process disclosed in U.S. Pat. Nos. 5,272,236 and5,278,272, the disclosures of which are incorporated herein byreference; and high pressure, free radical polymerized ethylene polymersand copolymers such as low density polyethylene (LDPE), ethylene-acrylicacid (EAA) and ethylene-methacrylic acid copolymers such as for examplethose available under the tradenames Primacor™ Nucrel™, and Escor™ anddescribed in U.S. Pat. Nos. 4,599,392, 4,988,781, and 5,384,373, each ofwhich is incorporated herein by reference in its entirety, andethylene-vinyl acetate (EVA) copolymers. Polymer compositions describedin U.S. Pat. Nos. 6,538,070, 6,566,446, 5,869,575, 6,448,341, 5,677,383,6,316,549, 6,111,023, or 5,844,045, each of which is incorporated hereinby reference in its entirety, are also suitable in some embodiments. Ofcourse, blends of polymers can be used as well. In some embodiments theblends include two different Ziegler-Natta polymers. In otherembodiments, the blends can include blends of a Ziegler-Natta and ametallocene polymer. In still other embodiments, the thermoplastic resinused herein is a blend of two different metallocene polymers.

In some particular embodiments, the thermoplastic resin is apropylene-based copolymer or interpolymer. In some embodiments, theprocess can be particularly well applied to propylene-based polymerssuch as for example those described in U.S. Pat. No. 5,504,172, U.S.Pat. No. 6,525,157 and WO 00/01745.

Any catalyst which is capable of copolymerizing one or more olefinmonomers to make an interpolymer or homopolymer may be used inembodiments of the invention. For certain embodiments, additionalselection criteria, such as molecular weight capability and/or comonomerincorporation capability, preferably should be satisfied. It should beunderstood that the term “catalyst” as used herein refers to ametal-containing compound which is used, along with an activatingcocatalyst, to form a catalyst system. The catalyst, as used herein, isusually catalytically inactive in the absence of a cocatalyst or otheractivating technique. However, not all suitable catalyst arecatalytically inactive without a cocatalyst and thus may not requireactivation.

Suitable catalysts include, but are not limited to, single-sitecatalysts (both metallocene catalysts and constrained geometrycatalysts), multi-site catalysts (Ziegler-Natta catalysts), andvariations therefrom. They include any known and presently unknowncatalysts for olefin polymerization. Ziegler-Natta-based processestypically also employ a Lewis acid as a catalyst activator. Somesuitable Lewis acids follow the formula R_(g)MX_(3-g) wherein R is R′ orOR′ or NR′₂ wherein R′ is a substituted or unsubstituted aliphatic oraromatic hydrocarbyl group containing 1 to 14 carbon atoms, X isselected from the group consisting of Cl, Br, I, and mixtures thereof,and g ranges from 0-3, and M is aluminum or boron. Exemplary Lewis acidsinclude tri-n-hexyl aluminum, triethyl aluminum, diethyl aluminumchloride, trimethyl aluminum, dimethyl aluminum chloride, methylaluminum dichloride, triisobutyl aluminum, tri-n-butyl aluminum,diiosbutyl aluminum chloride, isobutyl aluminum dichloride, (C₂H₅)AlCl₂,(C₂H₅O)AlCl₂, (C₆H₅)AlCl₂, (C₆H₅O)AlCl₂, (C₆H₁₃O)AlCl₂, and combinationsthereof. Exemplary boron-containing Lewis acids include B Cl₃, BBr₃,B(C₂H₅)Cl₂, B(OC₂H₅)Cl₂, B(OC₂H₅)₂Cl, B(C₆H₅)Cl₂, B(OC₆H₅)Cl₂,B(OC₆H₁₃)Cl₂, B(OC₆H₁₃)Cl₂, and B(OC₆H₅)₂Cl, and combinations thereof.

While any cocatalyst may be used, some suitable cocatalysts hereinfollow the formula AlX′_(d)(R″)_(c)H_(e) wherein X′ is Cl or OR′″, R″and R′″ are individually C₁ to C₁₄ saturated hydrocarbon radicals, d is0 to 1.5, e is 0 or 1; and c+d+e=3. Exemplary cocatalysts includeAl(CH₃)₃, Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(i-C₄H₉)₃, Al(C₂H₅)_(1.5)Cl_(1.5),Al(i-C₄H₉)₂H, Al(C₆H₁₃)₃, Al(C₈H₁₇)₃, Al(C₂H₅)₂H, Al(C₂H₅)₂(OC₂H₅), andcombinations thereof.

In some embodiments, a single site catalyst, such as a metallocenecatalyst, is used in the polymerization process. Single-site ormetallocene type catalysts often produce polymers that have uniquecharacteristics that are particularly useful in certain embodiments ofthe invention described herein. One suitable class of catalysts is theconstrained geometry catalysts disclosed in U.S. Pat. Nos. 5,064,802,5,132,380, 5,703,187, 6,034,021, EP 0 468 651, EP 0 514 828, WO93/19104, and WO 95/00526, all of which are incorporated by referencesherein in their entirety. Another suitable class of catalysts is themetallocene catalysts disclosed in U.S. Pat. Nos. 5,044,438; 5,057,475;5,096,867; and 5,324,800, all of which are incorporated by referenceherein in their entirety. It is noted that constrained geometrycatalysts may be considered as metallocene catalysts, and both aresometimes referred to in the art as single-site catalysts.

According to some embodiments of the invention, the process includescontacting ethylene and/or propylene and optionally one or morecomonomers with a catalyst in a suitable polymerization diluent. In oneembodiment, a chiral metallocene compound, e.g., a bis(cyclopentadienyl)metal compound as described in U.S. Pat. No. 5,198,401, and an activatorare used U.S. Pat. No. 5,391,629 also describes catalysts useful toproduce the some copolymers suitable in dispersions described herein.Gas phase polymerization processes are described in U.S. Pat. Nos.4,543,399, 4,588,790, 5,028,670, for example. Methods of supportingmetallocene catalysts useful for making some copolymers used inembodiments of the invention are described in U.S. Pat. Nos. 4,808,561,4,897,455, 4,937,301, 4,937,217, 4,912,075, 5,008,228, 5,086,025,5,147,949, and 5,238,892. Numerous examples of the biscyclopentadienylmetallocenes described above for the invention are disclosed in U.S.Pat. Nos. 5,324,800; 5,198,401; 5,278,119; 5,387,568; 5,120,867;5,017,714; 4,871,705; 4,542,199; 4,752,597; 5,132,262; 5,391,629;5,243,001; 5,278,264; 5,296,434; and 5,304,614. Descriptions of ioniccatalysts for coordination polymerization including metallocene cationsactivated by non-coordinating anions appear in the early work in EP-A-0277 003, EP-A-0 277 004, U.S. Pat. Nos. 5,198,401 and 5,278,119, and WO92/00333. The use of ionizing ionic compounds not containing an activeproton but capable of producing both the active metallocene cation and anon-coordinating anion is also known. See, EP-A-0 426 637, EP-A-0 573403 and U.S. Pat. No. 5,387,568, EP-A-0 427 697 and EP-A-0 520 732.Ionic catalysts for addition polymerization can also be prepared byoxidation of the metal centers of transition metal compounds by anionicprecursors containing metallic oxidizing groups along with the aniongroups; see EP-A-0 495 375.

Another suitable class of catalysts is substituted indenyl containingmetal complexes as disclosed in U.S. Pat. No. 5,965,756 and No.6,015,868 which are incorporated by reference herein in their entirety.Other catalysts are disclosed in copending applications: U.S. Pat. Nos.6,268,444 and 6,515,155 and U.S. Provisional Application Ser. No.60/215,456; No. 60/170,175, and No. 60/393,862. The disclosures of allof the preceding patent applications are incorporated by referenceherein in their entirety. These catalysts tend to have a highermolecular weight capability. Other catalysts, cocatalysts, catalystsystems, and activating techniques which may be used in the practice ofthe invention disclosed herein may include those disclosed in WO96/23010, published on Aug. 1, 1996, the entire disclosure of which ishereby incorporated by reference; those disclosed in WO 99/14250,published Mar. 25, 1999, the entire disclosure of which is herebyincorporated by reference; those disclosed in WO 98/41529, publishedSep. 24, 1998, the entire disclosure of which is hereby incorporated byreference; those disclosed in WO 97/42241, published Nov. 13, 1997, theentire disclosure of which is hereby incorporated by reference; thosedisclosed by Scollard, et al., in J. Am. Chem. Soc 1996, 118,10008-10009, the entire disclosure of which is hereby incorporated byreference; those disclosed in EP 0 468 537 B1, published Nov. 13, 1996,the entire disclosure of which is hereby incorporated by reference;those disclosed in WO 97/22635, published Jun. 26, 1997, the entiredisclosure of which is hereby incorporated by reference; those disclosedin EP 0 949 278 A2, published Oct. 13, 1999, the entire disclosure ofwhich is hereby incorporated by reference; those disclosed in EP 0 949279 A2, published Oct. 13, 1999, the entire disclosure of which ishereby incorporated by reference; those disclosed in EP 1 063 244 A2,published Dec. 27, 2000, the entire disclosure of which is herebyincorporated by reference; those disclosed in U.S. Pat. No. 5,408,017,the entire disclosure of which is hereby incorporated by reference;those disclosed in U.S. Pat. No. 5,767,208, the entire disclosure ofwhich is hereby incorporated by reference; those disclosed in U.S. Pat.No. 5,907,021, the entire disclosure of which is hereby incorporated byreference; those disclosed in WO 88/05792, published Aug. 11, 1988, theentire disclosure of which is hereby incorporated by reference; thosedisclosed in WO88/05793, published Aug. 11, 1988, the entire disclosureof which is hereby incorporated by reference; those disclosed in WO93/25590, published Dec. 23, 1993, the entire disclosure of which ishereby incorporated by reference; those disclosed in U.S. Pat. No.5,599,761, the entire disclosure of which is hereby incorporated byreference; those disclosed in U.S. Pat. No. 5,218,071, the entiredisclosure of which is hereby incorporated by reference; those disclosedin WO 90/07526, published Jul. 12, 1990, the entire disclosure of whichis hereby incorporated by reference; those disclosed in U.S. Pat. No.5,972,822, the entire disclosure of which is hereby incorporated byreference; those disclosed in U.S. Pat. No. 6,074,977, the entiredisclosure of which is hereby incorporated by reference; those disclosedin U.S. Pat. No. 6,013,819, the entire disclosure of which is herebyincorporated by reference; those disclosed in U.S. Pat. No. 5,296,433,the entire disclosure of which is hereby incorporated by reference;those disclosed in U.S. Pat. No. 4,874,880, the entire disclosure ofwhich is hereby incorporated by reference; those disclosed in U.S. Pat.No. 5,198,401, the entire disclosure of which is hereby incorporated byreference; those disclosed in U.S. Pat. No. 5,621,127, the entiredisclosure of which is hereby incorporated by reference; those disclosedin U.S. Pat. No. 5,703,257, the entire disclosure of which is herebyincorporated by reference; those disclosed in U.S. Pat. No. 5,728,855,the entire disclosure of which is hereby incorporated by reference;those disclosed in U.S. Pat. No. 5,731,253, the entire disclosure ofwhich is hereby incorporated by reference; those disclosed in U.S. Pat.No. 5,710,224, the entire disclosure of which is hereby incorporated byreference; those disclosed in U.S. Pat. No. 5,883,204, the entiredisclosure of which is hereby incorporated by reference; those disclosedin U.S. Pat. No. 5,504,049, the entire disclosure of which is herebyincorporated by reference; those disclosed in U.S. Pat. No. 5,962,714,the entire disclosure of which is hereby incorporated by reference;those disclosed in U.S. Pat. No. 5,965,677, the entire disclosure ofwhich is hereby incorporated by reference; those disclosed in U.S. Pat.No. 5,427,991, the entire disclosure of which is hereby incorporated byreference; those disclosed in WO 93/21238, published Oct. 28, 1993, theentire disclosure of which is hereby incorporated by reference; thosedisclosed in WO 94/03506, published Feb. 17, 1994, the entire disclosureof which is hereby incorporated by reference; those disclosed in WO93/21242, published Oct. 28, 1993, the entire disclosure of which ishereby incorporated by reference; those disclosed in WO 94/00500,published Jan. 6, 1994, the entire disclosure of which is herebyincorporated by reference; those disclosed in WO 96/00244, publishedJan. 4, 1996, the entire disclosure of which is hereby incorporated byreference; those disclosed in WO 98/50392, published Nov. 12, 1998, theentire disclosure of which is hereby incorporated by reference; thosedisclosed in Wang, et al., Organometallics 1998, 17, 3149-3151, theentire disclosure of which is hereby incorporated by reference; thosedisclosed in Younkin, et al., Science 2000, 287, 460-462, the entiredisclosure of which is hereby incorporated by reference; those disclosedby Chen and Marks, Chem. Rev. 2000, 100, 1391-1434, the entiredisclosure of which is hereby incorporated by reference; those disclosedby Alt and Koppl, Chem. Rev. 2000, 100, 1205-1221, the entire disclosureof which is hereby incorporated by reference; those disclosed byResconi, et al., Chem. Rev. 2000, 100, 1253-1345, the entire disclosureof which is hereby incorporated by reference; those disclosed by Ittel,et al., ChemRev. 2000, 100, 1169-1203, the entire disclosure of which ishereby incorporated by reference; those disclosed by Coates, Chem. Rev.,2000, 100, 1223-1251, the entire disclosure of which is herebyincorporated by reference; and those disclosed in WO 96/13530, publishedMay 9, 1996, the entire disclosure of which is hereby incorporated byreference. Also useful are those catalysts, cocatalysts, and catalystsystems disclosed in U.S. Ser. No. 09/230,185, filed Jan. 15, 1999; U.S.Pat. No. 5,965,756; U.S. Pat. No. 6,150,297; U.S. Ser. No. 09/715,380,filed Nov. 17, 2000. Methods for preparing the aforementioned catalystsare described, for example, in U.S. Pat. No. 6,015,868.

Some processes for olefin polymers such as polypropylene homopolymers orpropylene-based interpolymers employ a selectivity control agent (SCA)and are described in U.S. Pat. No. 5,093,415, No. 6,511,935 andWO2002096957, each of which is incorporated herein by reference in itsentirety. Typical SCAs are external electron donor compounds that can beused separately or partially or totally complexed with an activator,preferably an organoaluminum compound such as those described above.Many selectivity control agents are known in the art to produce activecatalysts. Illustrative suitable selectivity control agents includeelectron donors such as tetrahydrofuran and aromatic esters such asethyl benzoate or ethyl p-toluate, aromatic esters or organosilanes suchas alkylakoxysilanes and arylalkoxysilanes. Particularly suitablesilicon compounds of the invention contain at least onesilicon-oxygen-carbon linkage.

Regardless of the catalyst or activator, the polymerization is carriedout in the gas phase. It is preferably effected in a fluidized bedreactor or a stirred-tank reactor. Fluid bed reaction systems arediscussed in detail in U.S. Pat. Nos. 4,302,565 and 4,379,759 which areincorporated herein by reference in their entirety. However forconvenience, FIG. 1 illustrates an exemplary fluid bed reactor systemwhich can be used in embodiments of the invention. The reactor 10consists of a reaction zone 12 and a velocity reduction zone 14. Thereaction zone 12 comprises a bed of growing polymer particles, formedpolymer particles and a minor amount of catalyst particles fluidized bythe continuous flow of polymerizable and modifying gaseous components inthe form of make-up feed and recycle gas through the reaction zone. Themass gas flow rate through the bed is sufficient for fluidization. Gmfis used in the accepted form as the abbreviation for the minimum massgas flow required to achieve fluidization, C. Y. Wen and Y. H. Yu,“Mechanics of Fluidization,” Chemical Engineering Progress SymposiumSeries, Vol. 62, p. 100-111 (1966). In some embodiments the mass gasflow rate is 1.5, 3, 5, 7 or 10 times Gmf. The bed is prepared to avoidthe formation of localized “hot spots” and to entrap and distribute theparticulate catalyst throughout the reaction zone. On start up, thereaction zone is usually charged with a base of particulate polymerparticles before gas flow is initiated. Such particles may be identicalin nature to the polymer to be formed or different therefrom. Whendifferent, they are withdrawn with the desired formed polymer particlesas the first product. Eventually, a fluidized bed of the desired polymerparticles supplants the start-up bed.

The partially or completely activated precursor compound (the catalyst)used in the fluidized bed is preferably stored for service in areservoir 32 under a blanket of a gas which is inert to the storedmaterial, such as nitrogen or argon.

Fluidization is achieved by a high rate of gas recycle to and throughthe bed, typically in the order of about 50 times the rate of feed ofmake-up gas. The fluidized bed has the general appearance of a densemass of viable particles in possible free-vortex flow as created by thepercolation of gas through the bed. The pressure drop through the bed isequal to or slightly greater than the mass of the bed divided by thecross sectional area. It is thus dependent on the geometry of thereactor.

Make-up gas is generally fed to the bed at a rate equal to the rate atwhich particulate polymer product is withdrawn. The composition of themake-up gas is determined by a gas analyzer 16 positioned above the bed.The gas analyzer determines the composition of the gas being recycledand the composition of the make-up gas is adjusted accordingly tomaintain an essentially steady state gaseous composition within thereaction zone.

To insure proper fluidization, the recycle gas and where desired, partof the make-up gas are returned to the reactor at point 18 below thebed. There exists a gas distribution plate 20 above the point of returnto aid fluidizing the bed.

The portion of the gas stream which does not react in the bedconstitutes the recycle gas which is removed from the polymerizationzone, preferably by passing it into a velocity reduction zone 14 abovethe bed where entrained particles are given an opportunity to drop backinto the bed. Particle return may be aided by a cyclone 22 which may bepart of the recycle line. Where desired, the recycle gas may then bepassed through a preliminary heat exchanger 24 designed to cool smallentrained particles to prevent sticking in the downstream heat exchanger26.

The recycle gas is compressed in a compressor 25 and then passed througha heat exchanger 26 where it is stripped of heat of reaction before itis returned to the bed. By constantly removing heat of reaction, nonoticeable temperature gradient appears to exist within the upperportion of the bed. A temperature gradient exists in the bottom of thebed in a layer of about 6 to 12 inches, between the temperature of theinlet gas and the temperature of the remainder of the bed. Thus, it hasbeen observed that the bed acts to adjust the temperature of the recyclegas above this bottom layer of the bed zone to make it conform to thetemperature of the remainder of the bed thereby maintaining itself at anessentially constant temperature under steady state conditions. Therecycle is then returned to the reactor at its base 18 and to thefluidized bed through distribution plate 20. The compressor 25 can alsobe placed upstream of the heat exchanger 26.

The fluidized bed contains growing and formed particulate polymerparticles as well as catalyst particles. As the polymer particles arehot and possible active, they must be prevented from settling, for if aquiescent mass is allowed to exist, any active catalyst containedtherein may continue to react and cause fusion. Recycle gas is diffusedthrough the bed at a rate sufficient to maintain fluidization at thebase of the bed. The distribution plate 20 serves this purpose and maybe a screen, slotted plate, perforated plate, a plate of the bubble captype and the like. The elements of the plate may all be stationary, orthe plate may be of the mobile type disclosed in U.S. Pat. No.2,298,792. Whatever its design, it should diffuse the recycle gasthrough the particles at the base of the bed to keep them in a fluidizedcondition, and also serve to support a quiescent bed of resin particleswhen the reactor is not in operation. The mobile elements of the platemay be used to dislodge any polymer particles entrapped in or on theplate.

Hydrogen may be used as a chain transfer agent in the polymerizationreaction. The ratio of hydrogen/ethylene employed varies between about 0to about 2.0 moles of hydrogen per mole of the ethylene in the gasstream.

The gaseous feed streams of alpha-olefin(s), and hydrogen (optional) arepreferably fed to the reactor recycle line as well as liquidalpha-olefins and the cocatalyst solution. Optionally, the liquidcocatalyst can be fed directly to the fluidized bed. The partiallyactivated or completely activated catalyst precursor is preferablyinjected into the fluidized bed as a solid or a mineral oil slurry. Inthe case of partial activation, an activator can be added to thereactor. The product composition can be varied by changing the molarratios of the comonomers introduced into the fluidized bed. The productis continuously discharged in granular or particulate form from thereactor as the bed level builds up with polymerization. The productionrate is controlled in part by adjusting the catalyst feed rate.

The hydrogen/alpha-olefin molar ratio can be adjusted to control averagemolecular weights. In the case of a copolymer of ethylene, thealpha-olefins (other than ethylene) can be present in a total amount ofup to 15 percent by weight of the copolymer and, if used, are preferablyincluded in the copolymer in a total amount of about 0.3 to about 15percent by weight based on the weight of the copolymer.

The residence time of the mixture of reactants including gaseous andliquid reactants, catalyst, and resin in the fluidized bed can be in therange of about 1 to about 12 hours and is preferably in the range ofabout 2 to about 5 hours.

The total pressure in the fluidized bed reactor can be in the range ofabout 100 to about 600 psi (pounds per square inch), and is preferablyin the range of about 200 to about 450 psi. Partial pressure of theprimary alpha-olefin is set according to the amount of polymer desired.The balance of the total pressure is provided by alpha-olefins otherthan the primary alpha-olefin and/or inert gases such as nitrogen andinert hydrocarbons. The temperature in the reactors can be in the rangeof about 10 to about 130 degrees C., and is preferably in the range ofabout 50 to about 120 degrees C.

The reactor is run in the continuous mode in which granular polymer istypically withdrawn in 600 to 5000 pound shots while the polymerizationis in progress. In the continuous mode, the product discharge system isenabled after the bed weight typically builds to 40,000 to 180,000pounds, and the rate of discharge is altered to maintain constant bedweight.

As mentioned above, stirred tank reactors are also suitable in someembodiments of the invention. One such reactor is a two-phase(gas/solid) stirred bed, back mixed reactor. Some reactors are designedwith a set of four “plows” mounted horizontally on a central shaft.Preferably the shafts rotate at about 200 revolutions per minute (rpm)to keep the particles in the reactor mechanically fluidized. Thecylinder swept by these plows has a gas volume that is larger than themechanically fluidizable volume. A disengager vessel is mounted atop thevertical cylinder on the reactor. This vessel typically more thandoubles the gas volume of the reactor. Gas is continually recirculatedthrough both the reactor and disengager via a blower so that the gascomposition is homogeneous throughout.

Monomers and hydrogen (for molecular weight control) are fed to thereactor continuously via control valves. Partial pressures of monomertypically range between about 25 to about 400 psi. Comonomer (if any)content in the polymer is controlled by adjusting feed rates to maintaina constant comonomer/monomer molar ratio in the gas phase. Gascomposition is measured at 1 to 6 minute intervals by a gaschromatograph analyzer. Molecular weight of the polymer can becontrolled by adjusting hydrogen (optional) feed rate to maintain aconstant mole ratio of hydrogen to monomer in the gas phase. Nitrogenmakes up the balance of the composition of the gas, entering with thecatalyst and leaving via a small vent of the reactor gases. Vent openingis adjusted via computer to maintain constant total pressure in thereactor.

The reactor is cooled by an external jacket of chilled glycol. The bedtemperature is measured with an RTD temperature probe in a thermowellprotruding into the bed at a 60 degree angle below horizontal, betweenthe inner set of plows. Reactor temperature can be controlled to valuesin the range of about 10 to about 110 degrees C. Catalyst precursor canbe fed either dry or as a slurry. Dry catalyst precursor is metered inshots into a 0.5 to 1 pound per hour nitrogen stream and is fed to thereactor via a ⅛ inch tube. Slurry catalyst precursor is metered in shotsinto a continuous stream of either isopentane or cocatalyst/isopentanesolution in a ⅛ inch tube and this mixture is co-fed to the reactor witha 0.5 to 1 pound per hour nitrogen stream, which keeps polymer fromforming in the injection tube. In either case, the catalyst is injectedinto the bed at an angle of approximately 45 degrees below vertical intothe central zone between the front and rear plows.

The reactor is run in the continuous mode in which granular polymer istypically withdrawn in 0.4 pound shots while the polymerization is inprogress. In the continuous mode, the product discharge system isenabled after the bed weight typically builds to 15 to 25 pounds, andthe rate of discharge is altered to maintain constant bed weight.

A typical run in either reactor commences with monomers being charged tothe reactor and feeds adjusted until the desired gas composition isreached. An initial charge of cocatalyst is added prior to startingcatalyst feeding in order to scavenge any poisons present in thereactor. After catalyst feed starts, monomers are added to the reactorsufficient to maintain gas concentrations and ratios. Cocatalyst feedrate is maintained in proportion to the catalyst feed rate. A start-upbed may be used to facilitate stirring and dispersal of catalyst duringthe initial part of the operation. After the desired batch weight ismade, the reactor is immediately vented, and monomers are purged fromthe resin with nitrogen. The batch is then discharged into a box, opento the atmosphere, unless other catalyst deactivation measures arespecified. For multi-component operation, e.g., in situ blending, thedesired fraction of resin is prepared under the initial reactionconditions, the conditions are changed to the conditions appropriate forthe following stage of polymerization, and reaction is continued.

Conventional additives may also be introduced to the resins produced byembodiments of the invention. Some conventional additives include, forexample, antioxidants, ultraviolet absorbing compositions, anti-staticagents, pigments, dyes, nucleating agents, fillers, slip agents, fireretardants, plasticizers, smoke inhibitors, viscosity control agents,crosslinking agents and catalysts, tackifiers, and anti-blocking agents.Aside from fillers, the additives are typically present in the polymerresin in amounts of about 0.1 to about 10 parts by weight of theadditive for each 100 parts by weight of the resin. Fillers typicallyare added in amounts of about 200 parts by weight or more per 100 partsby weight of resin.

Many useful fabricated articles can be made from polymer resins made bythe processes described herein. For example, molding operations can beused to form useful fabricated articles or parts from the compositionsdisclosed herein, including various injection molding processes (e.g.,that described in Modern Plastics Encyclopedia/89, Mid October 1988Issue, Volume 65, Number 11, pp. 264-268, “Introduction to InjectionMolding” by H. Randall Parker and on pp. 270-271, “Injection MoldingThermoplastics” by Michael W. Green, the disclosures of which areincorporated herein by reference) and blow molding processes (e.g., thatdescribed in Modern Plastics Encyclopedia/89, Mid October 1988 Issue,Volume 65, Number 11, pp. 217-218, “Extrusion-Blow Molding” byChristopher Irwin, the disclosure of which is incorporated herein byreference), profile extrusion, calandering, pultrusion (e.g., pipes) andthe like. Rotomolded articles can also benefit from processes describedherein. Rotomolding techniques are well known to those skilled in theart and include, for example, those described in Modern PlasticsEncyclopedia/89, Mid October 1988 Issue, Volume 65, Number 11, pp.296-301, “Rotational Molding” by R. L. Fair, the disclosure of which isincorporated herein by reference).

Fibers (e.g., staple fibers, melt blown fibers or spunbonded fibers(using, e.g., systems as disclosed in U.S. Pat. Nos. 4,340,563,4,663,220, 4,668,566, or 4,322,027, all of which are incorporated hereinby reference), and gel spun fibers (e.g., the system disclosed in U.S.Pat. No. 4,413,110, incorporated herein by reference), both woven andnonwoven fabrics (e.g., spunlaced fabrics disclosed in U.S. Pat. No.3,485,706, incorporated herein by reference) or structures made fromsuch fibers (including, e.g., blends of these fibers with other fibers,e.g., PET or cotton) can also be made from compositions prepared by theembodiments of the processes disclosed herein.

Film and film structures can also be made from compositions prepared bythe processes described herein by using conventional hot blown filmfabrication techniques or other biaxial orientation processes such astenter frames or double bubble processes. Conventional hot blown filmprocesses are described, for example, in The Encyclopedia of ChemicalTechnology, Kirk-Othmer, Third Edition, John Wiley & Sons, New York,1981, Vol. 16, pp. 416-417 and Vol. 18, pp. 191-192, the disclosures ofwhich are incorporated herein by reference. Biaxial orientation filmmanufacturing process such as described in a “double bubble” process asin U.S. Pat. No. 3,456,044 (Pahlke), and the processes described in U.S.Pat. No. 4,352,849 (Mueller), U.S. Pat. No. 4,597,920 (Golike), U.S.Pat. No. 4,820,557 (Warren), U.S. Pat. No. 4,837,084 (Warren), U.S. Pat.No. 4,865,902 (Golike et al.), U.S. Pat. No. 4,927,708 (Herran et al.),U.S. Pat. No. 4,952,451 (Mueller), U.S. Pat. No. 4,963,419 (Lustig etal.), and U.S. Pat. No. 5,059,481 (Lustig et al.), the disclosures ofeach of which are incorporated herein by reference, can also be used tomake film structures. The film structures can also be made as describedin a tenter-frame technique, such as that used for orientedpolypropylene.

Other multi-layer film manufacturing techniques for food packagingapplications are described in Packaging Foods With Plastics, by WilmerA. Jenkins and James P. Harrington (1991), pp. 19-27, and in“Coextrusion Basics” by Thomas I. Butler, Film Extrusion Manual Process,Materials, Properties pp. 31-80 (published by TAPPI Press (1992)) thedisclosures of which are incorporated herein by reference.

The films may be monolayer or multilayer films. Film can also becoextruded with the other layer(s) or the film can be laminated ontoanother layer(s) in a secondary operation, such as that described inPackaging Foods With Plastics, by Wilmer A. Jenkins and James P.Harrington (1991) or that described in “Coextrusion For BarrierPackaging” by W. J. Schrenk and C. R. Finch, Society of PlasticsEngineers RETEC Proceedings, Jun. 15-17 (1981), pp. 211-229, thedisclosure of which is incorporated herein by reference. If a monolayerfilm is produced via tubular film (i.e., blown film techniques) or flatdie (i.e., cast film) as described by K. R. Osborn and W. A. Jenkins in“Plastic Films, Technology and Packaging Applications” (TechnomicPublishing Co., Inc. (1992)), the disclosure of which is incorporatedherein by reference, then the film must go through an additionalpost-extrusion step of adhesive or extrusion lamination to otherpackaging material layers to form a multilayer structure. If the film isa coextrusion of two or more layers (also described by Osborn andJenkins), the film may still be laminated to additional layers ofpackaging materials, depending on the other physical requirements of thefinal film. “Laminations Vs. Coextrusion” by D. Dumbleton (ConvertingMagazine (September 1992)), the disclosure of which is incorporatedherein by reference, also discusses lamination versus coextrusion.Monolayer and coextruded films can also go through other post extrusiontechniques, such as a biaxial orientation process.

Extrusion coating is yet another technique for producing multilayer filmstructures. Such coatings comprise at least one layer of the filmstructure. Similar to cast film, extrusion coating is a flat dietechnique. A sealant can be extrusion coated onto a substrate either inthe form of a monolayer or a coextruded extrudate.

Generally for a multilayer film structure, compositions made by theprocesses described herein comprise at least one layer of the totalmultilayer film structure. Other layers of the multilayer structureinclude but are not limited to barrier layers, and/or tie layers, and/orstructural layers. Various materials can be used for these layers, withsome of them being used as more than one layer in the same filmstructure. Some of these materials include: foil, nylon, ethylene/vinylalcohol (EVOH) copolymers, polyvinylidene chloride (PVDC), polyethyleneterephthalate (PET), oriented polypropylene (OPP), ethylene/vinylacetate (EVA) copolymers, ethylene/acrylic acid (EAA) copolymers,ethylene/methacrylic acid (EMAA) copolymers, LLDPE, HDPE, LDPE, nylon,graft adhesive polymers (e.g., maleic anhydride grafted polyethylene),and paper. Generally, the multilayer film structures comprise from 2 toabout 7 layers.

EXAMPLES Example 1

FIGS. 2 and 3 represent data generated by the procedure described inthis example which is carried out in a gas phase fluidized bed reactorusing a Ziegler-Natta catalyst. Ethylene partial pressure and reactorbed weight are controlled through predictive computer models andcoordinated control methods. The reactor is operated continuously withinthe following ranges:

Total reactor pressure: 19.8 to 21.0 bar absolute (289 to 273 psig)

Reactor bed temperature: 69.9 to 71.5 degrees C.

The alpha-olefins are propylene and ethylene. The gas composition, byweight, is 25.2 to 26.7 percent ethylene; 42.4 to 44.4 percentpropylene; 3.30 to 3.70 percent hydrogen; balance: nitrogen, ethane,methane, propane.

In this particular example, the ethylene partial pressure limit is setfrom a low of 4.0 bar absolute to a high of 8.0 bar absolute. The targetreactor bed weight operating point is set to 13,000 kilograms. Thereactor bed weight limit is selected to be at minus 500.0 kilograms to aplus 500.0 kilograms relative to the target reactor bed weight.

A desired resin production rate of 6,600 kilograms per hour is selectedand is allowed to vary in a range from about 6,600 to about 6,660kilograms per hour throughout the operating period as process conditionsallow different production rates. The actual production rate iscontinuously measured and the difference between the actual productionrate and desired production rate is determined.

From the difference between the actual and desired production rate, theethylene partial pressure of the reactor is varied from 5.1 to 6.50 barabsolute over the entire operating period. When production rate fallsbelow the rate desired, the ethylene partial pressure is increased, andwhen production rate rises above the rate desired, the ethylene partialpressure is decreased. All comparisons are based on predictivecalculations. The ethylene partial pressure is maintained within the 4.0to a high of 8.0 bar absolute limit established earlier. However, it isvaried to allow the reactor bed weight to return to its predeterminedtarget reactor bed weight operating point. In this example, the reactorbed weight varies, for periods of time, from the target value, but whenethylene partial pressure begins to have an effect on production rate,the ethylene partial pressure is moved back closer to the target. Itdoes not always return exactly to the target reactor bed weight becauseof changing process conditions such as poisons or catalyst differences,but the trend to return to target is present.

Over the operating period the reactor bed weight is on averageapproximately 30 kilograms less than the approximate average targetreactor bed weight. This is well within the limited range of minus 500.0to plus 500.0 kilograms around the target reactor bed weight whichindicates the reactor bed weight is kept near its target value fordesired reactor operation. If the reactor bed weight was the solecontrol variable for production rate, variation of reactor bed weightwould be expected to be much higher. Some of the offset of the actualreactor bed weight compared to the target reactor bed weight is alsotraced to the accuracy of predicted reactor bed weight effect onproduction rate compared to its actual effect on production rate. Fromthe difference between the actual and desired production rate andconsidering the effect of ethylene reactor bed weight, the reactor bedweight is varied from minus 500.0 kilograms to plus 500.0 kilogramsrelative to the target reactor bed weight kilograms over the entireoperating period. Based on production predictive calculations, thereactor bed weight is increased when the production rate is above thatdesired, and the reactor bed weight is decreased when the productionrate is below that desired. The reactor bed weight is maintained withinthe minus 500.0 kilograms to plus 500.0 kilograms limit relative to thetarget the reactor bed weight established in the first step.

The bed weight is controlled by adjusting the bed level or actual weightby adjusting the timing of product discharges to be faster or slower tomeet the desired bed weight. The amount of ethylene need to maintain theethylene partial pressure is determined. The ethylene is introduced (andcontrolled) into the reactor at needed flows to keep the reactorpressure and ethylene partial pressure near desired values.

The target reactor bed weight operating point is adjusted as indicatedby product and process analysis. In this case, reactor pressure,catalyst productivity, and resin density influence the target reactorbed weight operating point.

Example 2

FIGS. 3 and 4 represent data generated by the procedure described inthis example which is carried out in a gas phase fluidized bed reactor.A metallocene catalyst is used in the process. Catalyst flow rate andethylene partial pressure are controlled through predictive computermodels and coordinated control methods. The reactor is operatedcontinuously within the following ranges:

Total reactor pressure: 16.8 to 18.2 bar absolute (245 to 265 psig)

Reactor bed temperature: 75.0 to 85.0 degrees C.

The alpha-olefins are ethylene, hexene, and hydrogen. The gascomposition, by weight, is 58 to 52.5 percent ethylene; 0.68 to 73percent hexene; 278.0 to 302.0 part per million hydrogen; balance:nitrogen, ethane, methane, propane. Example 2 steps:

The catalyst feed limit is set to a low of 2.8 kilogram per hour to ahigh of 3.5 kilogram per hour. The ethylene partial pressure limit isselected to be at minus 0.14 bar-absolute to a plus 0.14 bar-absoluterelative to the target ethylene partial pressure. The target ethylenepartial pressure operating point is set to 10.3 bar-absolute.

Initially, a desired resin production rate of 3,600 kilograms per houris selected. The desired production rate is varied in a range from about3,250 kilograms per hour to about 4,400 kilograms per hour throughoutthe operating period as process conditions allow different productionrates.

The production rate is continuously measured. A difference between theactual and desired production rates is determined.

From the difference between the actual and desired production rate,catalyst feed is varied from 3.0 kilograms per hour to 3.3 kilograms perhour. When production rate falls below the rate desired, the catalystfeed is increased, and when production rate rises above the ratedesired, the catalyst feed is decreased. All comparisons are based onpredictive calculations. The catalyst feed is maintained within the lowof 3.0 kilogram per hour to a high of 3.5 kilogram per hour limitestablished earlier. However, it is varied to allow the ethylene partialpressure to return to its predetermined target ethylene partial pressureoperating point. In this example, the ethylene partial pressure varies,for periods of time, from the target value, but when ethylene partialpressure begins to have an effect on production rate, the ethylenepartial pressure is moved back closer to the target. It does not alwaysreturn exactly to the target ethylene partial pressure because ofchanging process conditions such as poisons or catalyst differences, butthe trend to return to target is present.

Over the operating period the ethylene partial pressure is varied fromabout 10.14 bar absolute to about 10.41 bar absolute and is on averageapproximately 0.06 bar-absolute less than the approximate average targetethylene partial pressure. This is well within the limited range ofminus 0.14 bar-absolute to a plus 0.14 bar-absolute around the targetethylene partial pressure which indicates the reactor bed weight is keptnear its target value for desired reactor operation. If the ethylenepartial pressure was the sole control variable for production rate,variation of ethylene partial pressure would be expected to be muchhigher. Some of the offset of the actual ethylene partial pressurecompared to the target ethylene partial pressure is also traced to theaccuracy of predicted ethylene partial pressure effect on productionrate compared to its actual effect on production rate. The ethylenepartial pressure is roughly maintained near the minus 0.14 bar-absoluteto a plus 0.14 bar-absolute limit relative to the target ethylenepartial pressure established in the first step.

The amount of ethylene needed to maintain the ethylene partial pressureis determined. The ethylene is introduced (and controlled) into thereactor at flows between 3,200 and 4,200 kilograms per hour to keep thereactor pressure and ethylene partial pressure near desired values andto satisfy the previous steps.

The target ethylene partial pressure operating point is adjusted asindicated by product and process analysis. In this case, reactorpressure and catalyst productivity influence the target ethylene partialpressure operating point.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. No single embodimentis representative of all aspects of the inventions. Moreover, variationsand modifications therefrom exist. For example, the processes describedherein may comprise other steps or may lack any particular step notexpressly enumerated herein. Some embodiments of the processes describedherein consist of or consist essentially of the enumerated processsteps. The appended claims intend to cover all such variations andmodifications as falling within the scope of the invention. In at leastsome embodiments, variation in resin properties or production rate maybe decreased by the methods described herein. Because of the decrease invariation, the likelihood of surges with the concomitant productioninterruption and degradation of resin properties is reduced andproduction rate can be increased. In addition, production rate and resinproperties can be kept closer to desired values.

1. A method of controlling a gas-phase polymerization process,comprising: (a) continuously, periodically or intermittently determininga difference between an actual or estimated value of a control variableand a desired value of the control variable; (b) adjusting ormaintaining at least a first manipulated variable to at least partiallycompensate for the difference between the actual or estimated value ofcontrol variable and the desired value; and (c) adjusting or maintaininga second manipulated variable to at least partially compensate for theeffect of adjusting or maintaining the first manipulated variable;wherein the first and second manipulated variables are selected from thegroup of process conditions consisting of a weight of fluidized bed, aconcentration of one or more monomers, a flow of one or more comonomers,a ratio of a first comonomer to a second comonomer, an first activatorconcentration, a ratio of a second activator to selectivity controlagent, a concentration of a chain transfer agent, and a retardantconcentration.
 2. A method of controlling a control variable of apolymerization reactor independent of controlling other polymerizationconditions in a gas-phase polymerization process, comprising: (a)continuously, periodically or intermittently determining a differencebetween an actual or estimated value of the control variable and adesired value of the control variable; (b) adjusting or maintaining atleast a first manipulated variable to at least partially compensate forthe difference between the actual or estimated value of the controlvariable and the desired value; and (c) adjusting or maintaining asecond manipulated variable to at least partially compensate for theeffect of adjusting or maintaining the first manipulated variable;wherein the first and second manipulated variables are selected from thegroup of process conditions consisting of a weight of fluidized bed, aconcentration of one or more monomers, a flow of one or more comonomers,a ratio of a first comonomer to a second comonomer, an first activatorconcentration, a ratio of a second activator to selectivity controlagent, a concentration of a chain transfer agent, and a retardantconcentration.
 3. The method of claim 1 wherein compensating for theeffect of adjusting the first manipulated variable further includescompensating for at least a portion of a remaining difference betweenthe actual or estimated value of the control variable and the desiredvalue.
 4. The method of claim 1, further including establishing limitson the value of the first manipulated variable.
 5. The method of claim1, wherein adjusting the second manipulated variable includescontinuously, periodically, or intermittently adjusting or maintainingthe second manipulated variable within a range having an upper and alower limit bounding a target value for second manipulated variable. 6.The method of claim 5, wherein the absolute value of the differencebetween the upper limit and the target value is different than theabsolute value between the lower limit and the target value.
 7. Themethod of claim 5, wherein the target value of the second manipulatedvariable is continuously, intermittently, or periodically adjusted. 8.The method of claim 1, wherein a change in the second manipulatedvariable affects the control variable relatively faster than a change inthe first manipulated variable.
 9. The method of claim 1, wherein thesecond manipulated variable is selected from the group consisting of theweight of fluidized bed, the activator concentration, and the retardantconcentration.
 10. The method of claim 1 wherein the control variable isthe production rate of the reactor.
 11. The method of claim 1 whereinthe control variable is a resin property selected from the groupconsisting of the molecular weight, the melt index, or molecular weightdistribution of the resin.
 12. The method of claim 1 where thepolymerization process includes a single site catalyst.
 13. The methodaccording to claim 1, wherein the first or second manipulated variableis the fluidized bed weight.
 14. The method according to any one of thepreceding claims, wherein the first and second manipulated variables areselected from the activator concentration and the fluidized bed weight.15. The method according to claim 1, wherein the first and secondmanipulated variables are selected from the concentration of one or moremonomers and the fluidized bed weight.
 16. The method according to claim1, wherein the first and second manipulated variables are selected fromthe fluidized bed weight and the retardant concentration.
 17. The methodaccording to claim 1, wherein the bed weight is maintained within about5% of a target bed weight.
 18. The method according to claim 1, whereinthe process forms an alpha-olefin homopolymer or interpolymer.
 19. Themethod according to claim 18, wherein the alpha-olefin homopolymer orinterpolymer comprises a polyethylene homopolymer or an interpolymer ofethylene with at least one comonomer selected from the group consistingof a C₄-C₂₀ linear, branched or cyclic diene, vinyl acetate, and acompound represented by the formula H₂C═CHR wherein R is a C₁-C₂₀linear, branched or cyclic alkyl group or a C₆-C₂₀ aryl group.
 20. Themethod according to claim 18, wherein the alpha-olefin homopolymer orinterpolymer comprises a polypropylene homopolymer or an interpolymer ofpropylene with at least one comonomer selected from the group consistingof ethylene, a C₄-C₂₀ linear, branched or cyclic diene, and a compoundrepresented by the formula H₂C═CHR wherein R is a C₁-C₂₀ linear,branched or cyclic alkyl group or a C₆-C₂₀ aryl group.